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In the Third Meditation (TM), Descartes introduces the doctrine of the « material falsehood » of ideas. In the Fourth Objections, Arnauld criticizes this doctrine which later disappears from Descartes’works. Recent interpretations have focussed on the coherence of the theory and compatibility between the wording of the TM and the Replies. Here, the topic is picked up again, bringing in the Scholastic debate on truth and falsehood. The presentation of Descartes’doctrine in the TM proves to be incompatible with that of the replies to Arnauld, suggesting an incompatibility of thetwo formulations of the doctrine of the « material falsehood » of ideas. Yet, the reason for Descartes’change of mind cannot be explained by the sole power of this criticism, since the conceptual framework of the Scholastic doctrine of representation offers Descartes the tools to defend his own doctrine without modifying it. Hence, the suggestion to look for the reasons of that change elsewhere, namely in Descartes’will to avoid the dangerous consequences for the foundations of scienceimplied by the TM’s formulation of thedoctrine of the « material falsehood » of ideas.